1. 11/14/2015 CHAPTER 10 Mendelian Genetics

2. 11/14/2015 MENDELIAN GENETICS Genetics - branch of biology that studies how genetic characteristics are inherited Genetics - branch of biology that studies how genetic characteristics are inherited First investigated by Gregor Mendel, an Augustinian monk (1822-1884) First investigated by Gregor Mendel, an Augustinian monk (1822-1884) His work was not accepted until 1900 (30 years later) His work was not accepted until 1900 (30 years later) The study of inheritance is often called Mendelian genetics. The study of inheritance is often called Mendelian genetics.

3. 11/14/2015 GENE INHERITANCE Diploid organisms have two forms of a gene – one from each parent Diploid organisms have two forms of a gene – one from each parent Several different forms (alleles) of each gene may exist within a population Several different forms (alleles) of each gene may exist within a population Alleles are found at the same location on a chromosome (called the locus) Alleles are found at the same location on a chromosome (called the locus) Ex: In humans there are two alleles for ear lobe shape (attached and unattached) Ex: In humans there are two alleles for ear lobe shape (attached and unattached)

4. 11/14/2015 Ear Lobe Shape

5. 11/14/2015 GENE INHERITANCE An organism’s genome is the set of all its genes. An organism’s genome is the set of all its genes. Genotype – genetic makeup of the organism Genotype – genetic makeup of the organism Phenotype – how alleles are expressed (physical characteristics) Phenotype – how alleles are expressed (physical characteristics) Alleles can be described as: Alleles can be described as: Dominant – trait that is expressed Dominant – trait that is expressed Designated by a capital letter (EE) Designated by a capital letter (EE) Recessive – trait is masked by dominant and not expressed Recessive – trait is masked by dominant and not expressed Designated by a lowercase letter (ee) Designated by a lowercase letter (ee)

6. 11/14/2015 GENE INHERITANCE Homozygous - alleles are of the same type Homozygous - alleles are of the same type both are dominant or both are recessive both are dominant or both are recessive AA, aa AA, aa Heterozygous – alleles are different Heterozygous – alleles are different one is dominant and the other is recessive one is dominant and the other is recessive Aa Aa

7. 11/14/2015 GENE INHERITANCE In homozygous individuals, the trait expressed depends on what alleles are present (AA, aa) In homozygous individuals, the trait expressed depends on what alleles are present (AA, aa) Heterozygous individuals are known as carriers: Heterozygous individuals are known as carriers: Only dominant allele is expressed or Only dominant allele is expressed or Trait will be expressed only under certain conditions Trait will be expressed only under certain conditions Ex: traits which are sex-linked Ex: traits which are sex-linked The environment also can determine whether or not a trait is expressed The environment also can determine whether or not a trait is expressed “nature vs. nurture” “nature vs. nurture”

8. 11/14/2015 Dark color in cats is expressed on the parts of the body that stay cool. The gene for freckles expresses itself more fully when a person is exposed to the sun.

9. 11/14/2015 GENE INHERITANCE: CODOMINANCE Both alleles are expressed (dominant) Both alleles are expressed (dominant) Ex: petal color in snapdragons Ex: petal color in snapdragons Homozygous plants (RR, WW) produce either red or white flowers Homozygous plants (RR, WW) produce either red or white flowers Heterozygous plants (RW) produce pink colored flowers Heterozygous plants (RW) produce pink colored flowers

10. 11/14/2015 GENE INHERITANCE: X-LINKED GENES Refers to genes found on X-chromosomes Refers to genes found on X-chromosomes Also called sex-linked genes Also called sex-linked genes These genes are inherited together because they are found on the same chromosome – called a linkage group These genes are inherited together because they are found on the same chromosome – called a linkage group Females get two copies of X-linked genes (XX), males get one copy (XY) Females get two copies of X-linked genes (XX), males get one copy (XY)

11. 11/14/2015 GENE INHERITANCE: X-LINKED GENES The Y is much smaller than the X chromosome, thus it has less genes. The Y is much smaller than the X chromosome, thus it has less genes. In men, because there is only one X, genes on the X-chromosomes will be expressed. In men, because there is only one X, genes on the X-chromosomes will be expressed. X-linked genes with abnormal traits are: X-linked genes with abnormal traits are: color blindness color blindness Hemophilia Hemophilia brown teeth brown teeth muscular dystrophy (Becker’s and Duchenne’s) muscular dystrophy (Becker’s and Duchenne’s) These are much more common in men These are much more common in men

12. 11/14/2015 SEX CHROMOSOMES

13. 11/14/2015 MENDEL’S LAW OF HEREDITY Gregor Mendel developed a method to predict inheritance Gregor Mendel developed a method to predict inheritance His work focused on: His work focused on: Garden peas - determined dominant and recessive traits Garden peas - determined dominant and recessive traits Obvious characteristics (Height, flower color, seed shape, etc.) Obvious characteristics (Height, flower color, seed shape, etc.) One trait at a time One trait at a time Lead to the development of three laws Lead to the development of three laws

14. 11/14/2015 MENDEL’S LAWS Law of dominance — an allele that is expressed over another allele is said to be dominant. Law of dominance — an allele that is expressed over another allele is said to be dominant. Law of segregation — during meiosis, alleles separate from one another into different gametes, retaining their individuality Law of segregation — during meiosis, alleles separate from one another into different gametes, retaining their individuality Law of independent assortment — members of one gene pair separate independently of other gene pairs Law of independent assortment — members of one gene pair separate independently of other gene pairs Do not apply to linked genes Do not apply to linked genes

15. 11/14/2015 PROBABILITY Genetic problems are based on probability Genetic problems are based on probability The chance that an event will happen The chance that an event will happen In monohybrid crosses, a single trait is studied. In monohybrid crosses, a single trait is studied. Crossing tall plants with short plants, green peas with yellow peas, etc. Crossing tall plants with short plants, green peas with yellow peas, etc. Punnett squares are tools that are used to determine probability Punnett squares are tools that are used to determine probability

16. 11/14/2015 MONOHYBRID CROSSES A tall pea plant crossed with a tall pea plant will produce offspring that are all tall A tall pea plant crossed with a tall pea plant will produce offspring that are all tall T T T T T T T

17. 11/14/2015 MONOHYBRID CROSSES A short pea plant crossed with a short pea plant will produce offspring that are all short A short pea plant crossed with a short pea plant will produce offspring that are all short t t t t t t t

18. 11/14/2015 MONOHYBRID CROSSES A tall pea plant crossed with a short pea plant will produce all tall offspring: A tall pea plant crossed with a short pea plant will produce all tall offspring: t t t t T T Tall is dominant - The phenotype is 100% tall. Tall is dominant - The phenotype is 100% tall. The genotype is 100% heterozygous tall (Tt) The genotype is 100% heterozygous tall (Tt) T t

19. 11/14/2015 MONOHYBRID CROSSES A heterozygous tall pea plant crossed with a heterozygous tall pea plant will produce varying offspring A heterozygous tall pea plant crossed with a heterozygous tall pea plant will produce varying offspring T t T t T T t t One will be homozygous tall, two will be heterozygous tall and one will be homozygous short. One will be homozygous tall, two will be heterozygous tall and one will be homozygous short. Genotypic ratio - 1:2:1 Genotypic ratio - 1:2:1 Phenotypic ratio - 3:1 (3 tall, 1 short) Phenotypic ratio - 3:1 (3 tall, 1 short) t t T t T

20. 11/14/2015 MONOHYBRID CROSSES: CODOMINANCE A red snapdragon (RR) crossed with a white snapdragon (WW) will produce offspring that are all pink A red snapdragon (RR) crossed with a white snapdragon (WW) will produce offspring that are all pink W W W W R R All offspring will be heterozygous, and because red and white are codominant, all the flowers will be pink. All offspring will be heterozygous, and because red and white are codominant, all the flowers will be pink. Genotypic ratio: all are heterozygous (RW ) Genotypic ratio: all are heterozygous (RW ) Phenotypic ratio: all are pink Phenotypic ratio: all are pink RW

21. 11/14/2015 MONOHYBRID CROSSES: CODOMINANCE A heterozygous pink crossed with a heterozygous pink, will produce varying offspring: A heterozygous pink crossed with a heterozygous pink, will produce varying offspring: W R W R W W R R One will be homozygous white, two will be heterozygous pink, and one will be homozygous red. One will be homozygous white, two will be heterozygous pink, and one will be homozygous red. The genotypic ratio will be 1:2:1 and the phenotypic ratio will also be 1:2:1. The genotypic ratio will be 1:2:1 and the phenotypic ratio will also be 1:2:1. RRRW WW

22. 11/14/2015 DIHYBRID CROSSES Two pairs of alleles are followed from parents to offspring. Two pairs of alleles are followed from parents to offspring. Crossing two individuals heterozygous for earlobes and color of hair, the gametes can combine in 16 different ways. Crossing two individuals heterozygous for earlobes and color of hair, the gametes can combine in 16 different ways. EeDd x EeDd EeDd x EeDd E – free earlobes; e – attached earlobes; D – dark hair; d – light hair E – free earlobes; e – attached earlobes; D – dark hair; d – light hair

23. 11/14/2015 DIHYBRID CROSSES ED Ed eD ed ED Ed eD ed ED ED Ed Ed eD eD ed ed The probability for a given phenotype will be 9:3:3:1. The probability for a given phenotype will be 9:3:3:1. 9 free earlobes, dark hair 9 free earlobes, dark hair 3 free earlobes, light hair 3 free earlobes, light hair 3 attached earlobes, dark hair 3 attached earlobes, dark hair 1 attached earlobes, light hair 1 attached earlobes, light hair eeddeeDdEeddEeDd eeDdeeDDEeDdEeDD EeddEeDdEEddEEDd EeDdEeDDEEDdEEDD

24. 11/14/2015 ALTERNATIVE INHERITANCE: MULTIPLE ALLELES Some genes are expressed by the presence of more than 2 alleles. Some genes are expressed by the presence of more than 2 alleles. Each person only gets two alleles, but in the population, there are more possibilities. Each person only gets two alleles, but in the population, there are more possibilities. ABO blood type in humans ABO blood type in humans Determined by 3 alleles (IA, IB, i) Determined by 3 alleles (IA, IB, i) 2 alleles are codominant, one is recessive 2 alleles are codominant, one is recessive GenotypePhenotype GenotypePhenotype IAIAtype A IAIAtype A IAitype A IAitype A IBIBtype B IBIBtype B IBitype B IBitype B IAIBtype AB IAIBtype AB iitype O iitype O

25. 11/14/2015 ALTERNATIVE INHERITANCE: POLYGENIC INHERITANCE Traits are determined by several genes at different loci Traits are determined by several genes at different loci Genes may be found on the same chromosome or on different chromosomes Genes may be found on the same chromosome or on different chromosomes Skin color in humans is an example Skin color in humans is an example Dark skin is dominant over light skin Dark skin is dominant over light skin 3 different loci for skin color 3 different loci for skin color Expressed as many possible variations Expressed as many possible variations

26. 11/14/2015 POLYGENIC INHERITANCE

27. 11/14/2015 ALTERNATIVE INHERITANCE: PLEIOTROPY Describes the multiple effects that a gene may have on a phenotype Describes the multiple effects that a gene may have on a phenotype Examples include PKU and Marfan Syndrome Examples include PKU and Marfan Syndrome PKU – a single gene affects many chemical reactions (autosomal recessive disorder) PKU – a single gene affects many chemical reactions (autosomal recessive disorder) Determines how a cell metabolizes phenylalanine (amino acid) Determines how a cell metabolizes phenylalanine (amino acid) Causes retardation if not treated with a proper diet Causes retardation if not treated with a proper diet Very light skin color Very light skin color

28. 11/14/2015 ALTERNATIVE INHERITANCE: PLEIOTROPY Marfan syndrome affects the connective tissue but can also affect other tissues (autosomal dominant disorder) Marfan syndrome affects the connective tissue but can also affect other tissues (autosomal dominant disorder) Symptoms include: Symptoms include: Disproportionately long arms, legs, and fingers Disproportionately long arms, legs, and fingers Skinniness and scoliosis of the spine Skinniness and scoliosis of the spine Myopia (near-sightedness) and dislocated lenses Myopia (near-sightedness) and dislocated lenses Weak or defective heart valves, aneurysms, and aortic dissections Weak or defective heart valves, aneurysms, and aortic dissections Collapsed lungs and sleep apnea Collapsed lungs and sleep apnea

29. 11/14/2015 MARFAN SYNDROME

30. 11/14/2015 ENVIRONMENTAL INFLUENCES Gene expression may vary on an individual basis Gene expression may vary on an individual basis Polydactylism (6 fingers) Polydactylism (6 fingers) Hormones on voice changes at puberty Hormones on voice changes at puberty Male-pattern baldness Male-pattern baldness PKU expression (proper diet prevents symptoms) PKU expression (proper diet prevents symptoms) Familial diabetes can be delayed by reducing sugar Familial diabetes can be delayed by reducing sugar Tanning Tanning

31. 11/14/2015 CHAPTER 10 Mendelian Genetics

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38. Dark color in cats is expressed on the parts of the body that stay cool. The gene for freckles expresses itself more fully when a person is exposed to the sun.

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46. T T T

47. 11/14/2015 t t t

48. 11/14/2015 T t

49. 11/14/2015 t t T t T

50. 11/14/2015 RW

51. 11/14/2015 RRRW WW

52. 11/14/2015

53. eeddeeDdEeddEeDd eeDdeeDDEeDdEeDD EeddEeDdEEddEEDd EeDdEeDDEEDdEEDD

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